So i have a bunch of new/new-to-me chisels which need to be flattened and sharpened. I found many of the chisels to have heavily concaved backs and need a lot of work to get flat. I was using 150 grit sandpaper, but it was taking too long and I was going through way too much sandpaper. I decided to change gears and ordered a Norton 220 grit waterstone. I did a fair amount of research before buying, and was aware that the stone would need to be flattened on a frequent basis. Even so, most conventional wisdom feels the waterstone would work faster and better than the sandpaper.Well, I have limited basis for comparison, but the waterstone does indeed work faster. BUT, this stone needs to be flattened way more often than I anticipated. It takes no time to turn the surface of the stone into a gouged-out wreck. I read that flattening on a 150-220 grit piece of sandpaper was effective. IMO, it is effective, but inefficient. I’m still going through a lot of sandpaper just to keep the stone flat. Saving sandpaper was a big part of my rationale for buying the stone. So it seems a coarse diamond stone might be needed to keep the waterstone flat. Of course, thise begs the question:Shouldn’t I have just bought a coarse diamond stone to begin with to flatten the chisels, and skipped the 220 grit waterstone?